Index: src/js/_enqueues/admin/common.js
===================================================================
--- src/js/_enqueues/admin/common.js	(revision 48902)
+++ src/js/_enqueues/admin/common.js	(working copy)
@@ -16,9 +16,338 @@
 	var $document = $( document ),
 		$window = $( window ),
 		$body = $( document.body ),
-		__ = wp.i18n.__;
+		__ = wp.i18n.__,
+		sprintf = wp.i18n.sprintf;
 
 /**
+ * Throws an error for a deprecated property.
+ *
+ * @since 5.5.1
+ *
+ * @param {string} propName    The property that was used.
+ * @param {string} version     The version of WordPress that deprecated the property.
+ * @param {string} replacement The property that should have been used.
+ */
+function deprecatedProperty( propName, version, replacement ) {
+	var message;
+
+	if ( 'undefined' !== typeof replacement ) {
+		message = sprintf(
+			/* translators: 1: Deprecated property name, 2: Version number, 3: Alternative property name. */
+			__( '%1$s is deprecated since version %2$s! Use %3$s instead.' ),
+			propName,
+			version,
+			replacement
+		);
+	} else {
+		message = sprintf(
+			/* translators: 1: Deprecated property name, 2: Version number. */
+			__( '%1$s is deprecated since version %2$s with no alternative available.' ),
+			propName,
+			version
+		);
+	}
+
+	window.console.error( message );
+}
+
+/**
+ * Deprecate all properties on an object.
+ *
+ * @since 5.5.1
+ *
+ * @param {string} name       The name of the object, i.e. commonL10n.
+ * @param {object} l10nObject The object to deprecate the properties on.
+ *
+ * @return {object} The object with all its properties deprecated.
+ */
+function deprecateL10nObject( name, l10nObject ) {
+	var deprecatedObject = {};
+
+	Object.keys( l10nObject ).forEach( function( key ) {
+		var prop = l10nObject[ key ];
+		var propName = name + '.' + key;
+
+		if ( 'object' === typeof prop ) {
+			Object.defineProperty( deprecatedObject, key, { get: function() {
+				deprecatedProperty( propName, '5.5.0', prop.alternative );
+				return prop.func();
+			} } );
+		} else {
+			Object.defineProperty( deprecatedObject, key, { get: function() {
+				deprecatedProperty( propName, '5.5.0', 'wp.i18n' );
+				return prop;
+			} } );
+		}
+	} );
+
+	return deprecatedObject;
+}
+
+window.wp.deprecateL10nObject = deprecateL10nObject;
+
+/**
+ * Removed in 5.5.0, needed for back-compatibility.
+ *
+ * @since 2.6.0
+ * @deprecated 5.5.0
+ */
+window.commonL10n = window.commonL10n || {
+	warnDelete: '',
+	dismiss: '',
+	collapseMenu: '',
+	expandMenu: ''
+};
+
+window.commonL10n = deprecateL10nObject( 'commonL10n', window.commonL10n );
+
+/**
+ * Removed in 5.5.0, needed for back-compatibility.
+ *
+ * @since 3.3.0
+ * @deprecated 5.5.0
+ */
+window.wpPointerL10n = window.wpPointerL10n || {
+	dismiss: ''
+};
+
+window.wpPointerL10n = deprecateL10nObject( 'wpPointerL10n', window.wpPointerL10n );
+
+/**
+ * Removed in 5.5.0, needed for back-compatibility.
+ *
+ * @deprecated 5.5.0
+ */
+window.userProfileL10n = window.userProfileL10n || {
+	warn: '',
+	warnWeak: '',
+	show: '',
+	hide: '',
+	cancel: '',
+	ariaShow: '',
+	ariaHide: ''
+};
+
+window.userProfileL10n = deprecateL10nObject( 'userProfileL10n', window.userProfileL10n );
+
+/**
+ * Removed in 5.5.0, needed for back-compatibility.
+ *
+ * @since 4.9.6
+ * @deprecated 5.5.0
+ */
+window.privacyToolsL10n = window.privacyToolsL10n || {
+	noDataFound: '',
+	foundAndRemoved: '',
+	noneRemoved: '',
+	someNotRemoved: '',
+	removalError: '',
+	emailSent: '',
+	noExportFile: '',
+	exportError: ''
+};
+
+window.privacyToolsL10n = deprecateL10nObject( 'privacyToolsL10n', window.privacyToolsL10n );
+
+/**
+ * Removed in 5.5.0, needed for back-compatibility.
+ *
+ * @since 3.6.0
+ * @deprecated 5.5.0
+ */
+window.authcheckL10n = {
+	beforeunload: ''
+};
+
+window.authcheckL10n = window.authcheckL10n || deprecateL10nObject( 'authcheckL10n', window.authcheckL10n );
+
+/**
+ * Removed in 5.5.0, needed for back-compatibility.
+ *
+ * @since 2.8.0
+ * @deprecated 5.5.0
+ */
+window.tagsl10n = {
+	noPerm: '',
+	broken: ''
+};
+
+window.tagsl10n = window.tagsl10n || deprecateL10nObject( 'tagsl10n', window.tagsl10n );
+
+/**
+ * Removed in 5.5.0, needed for back-compatibility.
+ *
+ * @since 2.5.0
+ * @deprecated 5.5.0
+ */
+window.adminCommentsL10n = window.adminCommentsL10n || {
+	hotkeys_highlight_first: {
+		alternative: 'window.adminCommentsSettings.hotkeys_highlight_first',
+		func: function() { return window.adminCommentsSettings.hotkeys_highlight_first; }
+	},
+	hotkeys_highlight_last: {
+		alternative: 'window.adminCommentsSettings.hotkeys_highlight_last',
+		func: function() { return window.adminCommentsSettings.hotkeys_highlight_last; }
+	},
+	replyApprove: '',
+	reply: '',
+	warnQuickEdit: '',
+	warnCommentChanges: '',
+	docTitleComments: '',
+	docTitleCommentsCount: ''
+};
+
+window.adminCommentsL10n = deprecateL10nObject( 'adminCommentsL10n', window.adminCommentsL10n );
+
+/**
+ * Removed in 5.5.0, needed for back-compatibility.
+ *
+ * @since 2.5.0
+ * @deprecated 5.5.0
+ */
+window.tagsl10n = window.tagsl10n || {
+	tagDelimiter: '',
+	removeTerm: '',
+	termSelected: '',
+	termAdded: '',
+	termRemoved: ''
+};
+
+window.tagsL10n = deprecateL10nObject( 'tagsl10n', window.tagsl10n );
+
+/**
+ * Removed in 5.5.0, needed for back-compatibility.
+ *
+ * @since 3.5.0
+ * @deprecated 5.5.0
+ */
+window.wpColorPickerL10n = window.wpColorPickerL10n || {
+	clear: '',
+	clearAriaLabel: '',
+	defaultString: '',
+	defaultAriaLabel: '',
+	pick: '',
+	defaultLabel: ''
+};
+
+window.wpColorPickerL10n = deprecateL10nObject( 'wpColorPickerL10n', window.wpColorPickerL10n );
+
+/**
+ * Removed in 5.5.0, needed for back-compatibility.
+ *
+ * @since 2.7.0
+ * @deprecated 5.5.0
+ */
+window.attachMediaBoxL10n = window.attachMediaBoxL10n || {
+	error: ''
+};
+
+window.attachMediaBoxL10n = deprecateL10nObject( 'attachMediaBoxL10n', window.attachMediaBoxL10n );
+
+/**
+ * Removed in 5.5.0, needed for back-compatibility.
+ *
+ * @deprecated 5.5.0
+ */
+window.postL10n = window.postL10n || {
+	ok: '',
+	cancel: '',
+	publishOn: '',
+	publishOnFuture: '',
+	publishOnPast: '',
+	dateFormat: '',
+	showcomm: '',
+	endcomm: '',
+	publish: '',
+	schedule: '',
+	update: '',
+	savePending: '',
+	saveDraft: '',
+	'private': '',
+	'public': '',
+	publicSticky: '',
+	password: '',
+	privatelyPublished: '',
+	published: '',
+	saveAlert: '',
+	savingText: '',
+	permalinkSaved: ''
+};
+
+window.postL10n = deprecateL10nObject( 'postL10n', window.postL10n );
+
+/**
+ * Removed in 5.5.0, needed for back-compatibility.
+ *
+ * @since 2.7.0
+ * @deprecated 5.5.0
+ */
+window.inlineEditL10n = window.inlineEditL10n || {
+	error: '',
+	ntdeltitle: '',
+	notitle: '',
+	comma: '',
+	saved: ''
+};
+
+window.inlineEditL10n = deprecateL10nObject( 'inlineEditL10n', window.inlineEditL10n );
+
+/**
+ * Removed in 5.5.0, needed for back-compatibility.
+ *
+ * @deprecated 5.5.0
+ */
+window.plugininstallL10n = window.plugininstallL10n || {
+	plugin_information: '',
+	plugin_modal_label: '',
+	ays: ''
+};
+
+window.plugininstallL10n = deprecateL10nObject( 'plugininstallL10n', window.plugininstallL10n );
+
+/**
+ * Removed in 5.5.0, needed for back-compatibility.
+ *
+ * @deprecated 5.5.0
+ */
+window.navMenuL10n = window.navMenuL10n || {
+	noResultsFound: '',
+	warnDeleteMenu: '',
+	saveAlert: '',
+	untitled: ''
+};
+
+window.navMenuL10n = deprecateL10nObject( 'navMenuL10n', window.navMenuL10n );
+
+/**
+ * Removed in 5.5.0, needed for back-compatibility.
+ *
+ * @since 2.5.0
+ * @deprecated 5.5.0
+ */
+window.commentL10n = window.commentL10n || {
+	submittedOn: '',
+	dateFormat: ''
+};
+
+window.commentL10n = deprecateL10nObject( 'commentL10n', window.commentL10n );
+
+/**
+ * Removed in 5.5.0, needed for back-compatibility.
+ *
+ * @deprecated 5.5.0
+ */
+window.setPostThumbnailL10n = window.setPostThumbnailL10n || {
+	setThumbnail: '',
+	saving: '',
+	error: '',
+	done: ''
+};
+
+window.setPostThumbnailL10n = deprecateL10nObject( 'setPostThumbnailL10n', window.setPostThumbnailL10n );
+
+
+/**
  * Removed in 3.3.0, needed for back-compatibility.
  *
  * @since 2.7.0
Index: src/js/_enqueues/wp/theme-plugin-editor.js
===================================================================
--- src/js/_enqueues/wp/theme-plugin-editor.js	(revision 48902)
+++ src/js/_enqueues/wp/theme-plugin-editor.js	(working copy)
@@ -1000,3 +1000,19 @@
 
 	return component;
 })( jQuery );
+
+wp.themePluginEditor.l10n = wp.themePluginEditor.l10n || {
+	saveAlert: '',
+	saveError: '',
+	lintError: {
+		alternative: 'wp.i18n',
+		func: function() {
+			return {
+				singular: '',
+				plural: ''
+			};
+		}
+	}
+};
+
+wp.themePluginEditor.l10n = window.wp.deprecateL10nObject( 'wp.themePluginEditor.l10n', wp.themePluginEditor.l10n );
Index: src/js/_enqueues/wp/updates.js
===================================================================
--- src/js/_enqueues/wp/updates.js	(revision 48902)
+++ src/js/_enqueues/wp/updates.js	(working copy)
@@ -43,6 +43,81 @@
 	wp.updates = {};
 
 	/**
+	 * Removed in 5.5.0, needed for back-compatibility.
+	 *
+	 * @since 4.2.0
+	 * @deprecated 5.5.0
+	 *
+	 * @type {object}
+	 */
+	wp.updates.l10n = {
+		searchResults: '',
+		searchResultsLabel: '',
+		noPlugins: '',
+		noItemsSelected: '',
+		updating: '',
+		pluginUpdated: '',
+		themeUpdated: '',
+		update: '',
+		updateNow: '',
+		pluginUpdateNowLabel: '',
+		updateFailedShort: '',
+		updateFailed: '',
+		pluginUpdatingLabel: '',
+		pluginUpdatedLabel: '',
+		pluginUpdateFailedLabel: '',
+		updatingMsg: '',
+		updatedMsg: '',
+		updateCancel: '',
+		beforeunload: '',
+		installNow: '',
+		pluginInstallNowLabel: '',
+		installing: '',
+		pluginInstalled: '',
+		themeInstalled: '',
+		installFailedShort: '',
+		installFailed: '',
+		pluginInstallingLabel: '',
+		themeInstallingLabel: '',
+		pluginInstalledLabel: '',
+		themeInstalledLabel: '',
+		pluginInstallFailedLabel: '',
+		themeInstallFailedLabel: '',
+		installingMsg: '',
+		installedMsg: '',
+		importerInstalledMsg: '',
+		aysDelete: '',
+		aysDeleteUninstall: '',
+		aysBulkDelete: '',
+		aysBulkDeleteThemes: '',
+		deleting: '',
+		deleteFailed: '',
+		pluginDeleted: '',
+		themeDeleted: '',
+		livePreview: '',
+		activatePlugin: '',
+		activateTheme: '',
+		activatePluginLabel: '',
+		activateThemeLabel: '',
+		activateImporter: '',
+		activateImporterLabel: '',
+		unknownError: '',
+		connectionError: '',
+		nonceError: '',
+		pluginsFound: '',
+		noPluginsFound: '',
+		autoUpdatesEnable: '',
+		autoUpdatesEnabling: '',
+		autoUpdatesEnabled: '',
+		autoUpdatesDisable: '',
+		autoUpdatesDisabling: '',
+		autoUpdatesDisabled: '',
+		autoUpdatesError: ''
+	};
+
+	wp.updates.l10n = window.wp.deprecateL10nObject( 'wp.updates.l10n', wp.updates.l10n );
+
+	/**
 	 * User nonce for ajax calls.
 	 *
 	 * @since 4.2.0
Index: src/wp-includes/script-loader.php
===================================================================
--- src/wp-includes/script-loader.php	(revision 48902)
+++ src/wp-includes/script-loader.php	(working copy)
@@ -1013,7 +1013,7 @@
 	$scripts->add( 'htmlhint', '/wp-includes/js/codemirror/htmlhint.js', array(), '0.9.14-xwp' );
 	$scripts->add( 'htmlhint-kses', '/wp-includes/js/codemirror/htmlhint-kses.js', array( 'htmlhint' ) );
 	$scripts->add( 'code-editor', "/wp-admin/js/code-editor$suffix.js", array( 'jquery', 'wp-codemirror', 'underscore' ) );
-	$scripts->add( 'wp-theme-plugin-editor', "/wp-admin/js/theme-plugin-editor$suffix.js", array( 'wp-util', 'wp-sanitize', 'jquery', 'jquery-ui-core', 'wp-a11y', 'underscore' ) );
+	$scripts->add( 'wp-theme-plugin-editor', "/wp-admin/js/theme-plugin-editor$suffix.js", array( 'common', 'wp-util', 'wp-sanitize', 'jquery', 'jquery-ui-core', 'wp-a11y', 'underscore' ) );
 	$scripts->set_translations( 'wp-theme-plugin-editor' );
 
 	$scripts->add( 'wp-playlist', "/wp-includes/js/mediaelement/wp-playlist$suffix.js", array( 'wp-util', 'backbone', 'mediaelement' ), false, 1 );
@@ -1261,7 +1261,7 @@
 		$scripts->add( 'privacy-tools', "/wp-admin/js/privacy-tools$suffix.js", array( 'jquery', 'wp-a11y' ), false, 1 );
 		$scripts->set_translations( 'privacy-tools' );
 
-		$scripts->add( 'updates', "/wp-admin/js/updates$suffix.js", array( 'jquery', 'wp-util', 'wp-a11y', 'wp-sanitize' ), false, 1 );
+		$scripts->add( 'updates', "/wp-admin/js/updates$suffix.js", array( 'common', 'jquery', 'wp-util', 'wp-a11y', 'wp-sanitize' ), false, 1 );
 		$scripts->set_translations( 'updates' );
 		did_action( 'init' ) && $scripts->localize(
 			'updates',